[simulo]

This is very similar to what Grudin suggests in his HCI history "From tool to partner": Apple used to be very usability and research focussed in the 80s and early 90s, but turned away from it with Jobs and went more look-driven — and had great success with it. Other companies followed. (Which does not mean that companies ignored graphic design before, but it was the more utilitarian parts of graphic design that were important focussing on distinct shapes, readability etc.)

[api]

True but I don’t think this gets it quite right.

The big problem with classic Mac was the cooperative multitasking weird OS and the unstylish and clunky hardware. The UI needed polish and modernization but was not fundamentally bad.

The complete loss of OS coherence has a lot more to do with the web than anything else.